Conclusion

So, does it work? Quite well actually. At first I was planning on just converting the
4 GameBoy Classic sound channels to MIDI, but it seems I've ran away with the concept
a bit... The end result is quite nice, though, there are lots of sounds to be gotten
from the little GBA and it actually has become a fun-to-use little and cheap
synthesizer.

For example, I gave my friend Robert (better known as the guy behind
Klontart on the Internet) the prototype I made.
As you can see on his
website, he has quite a lot more experience with music and synthesizers than I have.
He connected the GBA to some of his studio equipment and the combination of all the
hardware and about two hours of composing resulted in a delightfully cheesy tune,
to which you can listen on his
Soundcloud page.

As usual, the firmware for both the AVR- and the GBA-code is open-source
and can be downloaded here. At the moment,
it's supposed to run on an ATMega168 and almost completely fills up that chip.
If you want to add functionality, I'd suggest getting it to run on an ATMega328 first.
Also, the AVRs code is supposed to be in the bootloader section of the AVR, making
it difficult to port this code to an Arduino, which has its own bootloader. With a bit
of swapping around and losing the midi firmware update function, it could be made
to work though.

If you download the code and improve or add stuff, please do
drop me a line.
Also, I really like chiptunes, so if you manage to push a cool song out of my
contraption, I'd really appreciate a link. Happy composing!

To everyone wanting to buy one: I've implemented this in an interface which is now available for sale on my website: https://catskullelectronics.com/gbamidi
If you have any questions, just email me at bro at catskull dot net!

Robbie wrote at 24 Nov 2017, 1.46:

Thanks a ton! If you could do that, it would be awesome :)

Sprite_tm wrote at 19 Nov 2017, 15.26:

No - I should make the sources and designs for the more advanced version I sold open-source at some point in time, though - less bugs and more functionality in that.

Robbie wrote at 14 Nov 2017, 0.49:

Hey Sprite, would you mind a young starving hacker making and selling these? I guess I can not improve anything in your code, as my skills are way far from yours. Bu I may try to make a USB version.

Alex wrote at 27 Oct 2017, 4.04:

I'd love to know if you're still selling the cable. If so, how much? jalexbeatz@gmail.com

Jack wrote at 17 May 2016, 3.57:

I would love to buy one. Are you selling them? dodgerweiss@gmail.com

Jean Henrique wrote at 24 Jan 2016, 21.45:

Hello, I'm planning to build a cable for a project but I have two questions. First, does the code respond to MIDI channel 10 (drums) as white noise or as square wave? Second, I read that the GBA I/O's work at 3.3v, so as the Atmega168 runs on the 5v from MIDI IN, shouldn't it damage the GBA?

roman wrote at 18 Dec 2015, 17.54:

I would love to buy one cable. do you still have one to sell? thnx -- lowfi@ciencias.unam.mx

Frostbite wrote at 15 Dec 2015, 7.01:

Hello! I would like to know if you are still selling the cable? If so tell me how much:
djfrostbite@hotmail.ca

melomb wrote at 4 Mar 2015, 21.18:

hello,please if you can sell a cable please let me now. melo9211@gmail.com

Matty wrote at 24 Jan 2015, 21.00:

Are you guys still making these I'm a retro gamer who wants to branch of in to retro music I make if u are selling them please email. m.Salisbury@hotmail.co.uk

simon wrote at 5 Nov 2014, 12.12:

Any of these still in existance? I'd really like to buy one. simonhowden3010@gmail.com

I was wondering if you have any of these for sale still. My email is skarudieska@gmail.com

Tyler wrote at 2 Aug 2013, 9.55:

Alright so I'm trying to build one of these myself and I'm confused about how to get the code onto my ATmega168. Is all I have to do is upload the .hex file that is already included, or do I have to do all this makefile compiling business?

Tyler wrote at 26 Jul 2013, 0.43:

Hmmm. I'm guessing this wont work on Arduino Mini Pro without some modifications right? What is the easiest/cheapest way of uploading this code to an ATmega168? Or have you figured out a way to port this to arduino yet? Better yet, are you still selling these? bassmonster138@hotmail.com

RunnerPack wrote at 18 Jun 2013, 6.17:

This rocks, Sprite_tm! Seriously: one of your best projects, to date (and that's saying something)!
I have a Wii Rock Band 2 keyboard which is only useful as a MIDI controller, since I got it 2nd hand and it didn't include the receiver. I also have the guts of a GBA lying around. Think of the beautiful irony of building them into a "Nintendo-themed", self-contained, "chiptune" instrument!
To this end, would anyone be willing to sell me just the pre-programmed AVR? (DIP, for preference, since my "dead-bug" skills aren't /quite/ up to Sprite standards, yet ;). Let me know via my above username at GMail. Thanks!

anibal wrote at 2 Jun 2013, 11.47:

do you have any of those cables for sale?
anibal.salcedo@hotmail.com

Sr_Pixel wrote at 24 May 2013, 2.55:

Good job buddy, sounds beautiful :).

James wrote at 28 Mar 2013, 22.36:

Nicely done. Flash carts and programmers for the original gameboy (they work in the GBA too) are actually not too hard to do. I've built several recently, as well as a programmer with a USB interface, they work perfectly well.
I used a design I found here: http://www.ziegler.desaign.de/readplus.htm

Josiah wrote at 30 Oct 2012, 18.44:

I would also like one, if they are available. JTMAsteller@gmail.com

kevin wrote at 15 Aug 2012, 6.08:

do you still have any for sale? i am interested
my email is maththeband@gmail.com

patrick wrote at 21 Jun 2012, 13.03:

brilliant. i will try to build this myself after i finish my bachelor thesis

culinary wrote at 10 Jun 2012, 13.43:

It's beautiful. This is by far the most useful GBA hack I've seen, and just what I was looking for. I wonder if I could get an ATmega644 to do all this while being the MIDI device itself rather than taking MIDI input. I'll get to work on that right away.

Sprite_tm wrote at 2 Apr 2012, 9.59:

mitch: I actually do sell them; I whipped up a small batch of them and I still have a few left. Contact me (using the link at the very bottom of this page) if you want one.

mitch wrote at 30 Mar 2012, 13.24:

wow. Amazing. Wish you sold these! :P

Average producer wrote at 9 Feb 2012, 7.11:

I love how this thing sounds, but I'm hopeless to make one. I compose chipmusic, and it would be awesome to have this in my setup. I'm trying to convince a friend to make one for me.

jonny wrote at 26 Jan 2012, 22.31:

does anyone know how to make this using arduino? If they do they should make an easy to understand guide for the "somewhat" technical people looking to do this project.

bram wrote at 17 Jan 2012, 21.01:

is it possible to connect multiple game-boys to the atmega let's say 3 that would be cool

Gdogg wrote at 1 Oct 2011, 3.38:

I read this pretty much the day it came out, but I must have been tired or something. Just re-read it now and it's fantastic.
Also listening to your friend's stuff right now. Other than some of it making me think my cat is meowing outside, I like it :)
Keep it up!

anonymous wrote at 29 Aug 2011, 5.04:

I didn't know a Gameboy could do something like that! Absolutely amazing! Wonder if it would work with my old Sound Blaster...